Nowadays, multiple Global Navigation Satellite System (GNSS) are available, including GPS (Global Positioning System) of US, which is designed to have 32 operational satellites, Galileo of Europe, which is designed to have 27 operational satellites, GLONASS (GLObal NAvigation Satellite System) of USSR (and later Russia), which is designed to have 24 operational satellites, and Compass of China, which is designed to have 35 operational satellites. The constellation composed of these systems is called super GNSS constellation. In addition Regional Navigation Satellite Systems (RNSS) such as QZSS (Quasi-Zenith Satellite System) of Japan and GAGAN (GPS Aided Augmented Navigation System) of India are also planed to be operable in the near future.
Further, various SBAS (Satellite Based Augmentation Systems) have been developed to augment GNSS, such as WAAS (Wide Area Augmentation System) of US, EGNOS (European Geostationary Navigation Overlay Service) of Europe, MSAS (MTSAT Satellite Based Augmentation System) of Japan, and GAGAN of India.
As can been seen, the current constellation of satellites has been quite dense. As can be easily expected, the sky will be crowded with more and more satellites in the coming future. Therefore, how to search all the satellites quickly becomes more and more challenging for a receiver. As known in this field, searching for a satellite is to determine its satellite ID, Doppler frequency and PRN (Pseudo Random Number) code phase. The hardware speedup for the receiver is usually performed to reduce searching time in acquisition of Doppler frequency and PRN code phase. Little attention has been given to deal with the unknown satellite IDs. As mentioned, there are more and more satellite IDs to try in the satellite search as the constellation becomes larger and larger. It will take a very long period of time to acquire all the visible satellites by using the conventional sequential search method. In such a conventional method, the satellites are searched one by one and in a fixed sequence. The present invention provides a solution to overcome this problem.